Referring to FIG. 1, a conventional blind assembly having no pull cord is shown to include an upper beam 11 defining a receiving space 111; a blind body 12 disposed on the bottom of the upper beam 11; a fixed seat 13, a movable seat 14 and a cord-winding controller 15 all disposed in the receiving space 111; and a plurality of lift cords 16, each of which passes through the blind body 12 and winds around the fixed seat 13 and the movable seat 14. The cord-winding controller 15 includes a rotating seat 151 having a rotating shaft 150, two torsion springs 152 respectively disposed on two opposite sides of the rotating shaft 150, and a drive cord 153 wound around the rotating seat 151 and having one end fixed to the movable seat 14. When the blind body 12 is pushed or pulled by an external force, the torsion springs 152 provide torsion for driving the rotating seat 151 to wind or unwind the drive cord 153. The drive cord 153, in turn, drives a sliding movement of the movable seat 14 for linking movement of the lift cords 16. An extent to which the blind body 12 is raised or lowered can thus be adjusted. However, during operation, the torsion springs 152 will wind reversely around the rotating shaft 150, resulting in a large deformation thereof, so that the service life of the torsion springs 152 is shortened. Moreover, this conventional blind assembly uses many components and complex coordination among the components, so that the assembly thereof is inconvenient, and the cost is high.
Referring to FIG. 2, another conventional blind assembly is shown to include a tabular support frame 21, a foldable blind body 22 having a top edge mounted to the support frame 21, a pulley seat 23 mounted slidably on the support frame 21, two first pulleys 24 mounted on the support frame 21, two second pulleys 25 mounted on the pulley seat 23, and a tension spring 26 and a lift cord 27 each of which is connected to the support frame 21 and the pulley seat 23. The support frame 21 includes opposite first and second ends 211, 212, a first end cap 213 mounted on the first end 211, and a second end cap 214 mounted on the second end 212 for fixing the tension spring 26. The lift cord 27 has a fixed intermediate section 271 fixed to the first end cap 213, and two cord end sections 272 extending outwardly and respectively from two opposite ends of the fixed intermediate section 271. The cord end sections 272 wind through the first and second pulleys 24, 25, and pass through the support frame 21 and the blind body 22 to be fixed on a lower end of the blind body 22. When the lower end of the blind body 22 is pulled or pushed by an external force, the lift cord 27 is driven to move, the first and second pulleys 24, 25 are driven to rotate, and the pulley seat 23 is driven to slide, so that the tension spring 26 is compressed or uncompressed to raise or lower the blind body 22. Hence, the effect of adjusting the blind body 22 having no pull cord can be achieved. However, the tension spring 26 requires a sufficient tension space. If the apace is too short, the elastic force of the tension spring 26 will be insufficient; and if the space is too long, it will result in elastic fatigue of the tension spring 26. The length of the tubular support frame 21 is thus restricted. Further, when the tension of the tension spring 26 is increased, the elastic force thereof is also increased, so that there is a big difference in the pulling force of the tension spring 26 before and after tensioning. Thus, the pulling force of the tension spring 26 may not be balanced with the weight, of the blind body 22. Moreover, more effort is necessary to pull the blind body 22 downward, so that if excessive force is used to pull down the blind body 22, the blind body 22 may likely get damaged. Hence, the conventional blind assembly is inconvenient to use.